Multi-layer golf ball providing improved speed

ABSTRACT

The present invention is directed to a multi-layer golf ball comprising at least one core or core layer, at least one intermediate layer, and at least one cover layer. The core has a diameter of about 1.20 to about 1.56 in. and a PGA compression of about 40 to about 90. The intermediate layer comprises a modified ionomeric polymer, and it has a thickness of about 0.01 to about 0.10 in. and a Shore D hardness of about 30 to about 70. The cover layer has a Shore D hardness of about 40 to about 75. The multi-layer golf balls of the present invention provide high driver ball speed and/or a high Coefficient of Restitution, while maintaining excellent shot feel.

CROSS-REFERENCE TO RELATED APPLICATIONS

Priority is claimed under 35 U.S.C. §119(e) to U.S. Provisional PatentApplication No. 60/572,432, filed on May 19, 2004, entitled “Multi-LayerGolf Ball Providing Improved Speed,” by Dean A. Snell, Hyun Jin Kim andEric Loper, which application is incorporated by reference herein.

BACKGROUND OF THE INVENTION

This invention relates generally to golf balls, and, more specifically,to multi-layer golf balls. In particular, this invention relates to agolf ball having a core, at least one intermediate layer, and at leastone cover layer, wherein the intermediate layer comprises an ionomer, orionomer blend, and further comprises at least one fatty acid or metalsalt thereof. The multi-layer golf balls of the present inventionprovide a higher ball speed and/or a higher coefficient of restitution(“C.O.R.”) than do analogous balls having an identical core and coverlayer, but an intermediate layer made from the identical ionomers orionomer blends but lacking the fatty acid or metal salt.

Until recently, golf balls typically were divided into two general typesor groups: 1) two-piece balls, and 2) wound balls (also known asthree-piece balls). The difference in the play characteristics of thesetwo types of balls can be quite significant.

Wound balls typically have either a solid rubber, or liquid-filled,center around which many yards of a stretched elastic thread or yarn iswound to form a core. The wound core then is covered with a durablecover material, e.g., an ionomer or other thermoplastic material or asofter cover such as balata or cast polyurethane. Wound balls generallyare softer than two-piece balls, and they provide more spin, whichenables a skilled golfer to have more control over the ball's flight. Inparticular, it is desirable for the golfer to be able to impart backspinto the ball, for purposes of controlling its flight and controlling theaction of the ball upon landing on the ground. For example, substantialbackspin will make the ball stop once it strikes the landing surfaceinstead of bounding forward. The ability to impart backspin onto a golfball is related to the extent to which the golf ball's cover deformswhen it is struck by a golf club. Because conventional wound balls aregenerally more deformable than are conventional two-piece balls, it iseasier to impart spin to wound balls. However, higher spinning woundballs typically travel a shorter distance when struck, as compared totwo-piece balls. Moreover, because wound balls generally have a morecomplex structure, they generally require a longer time to manufactureand are more expensive to produce than are two-piece balls.

Golf balls having a two-piece construction generally are most popularwith the recreational golfer, because they are relatively durable andprovide maximum distance. Two-piece balls have a single solid core,usually formed of a cross-linked rubber, which is encased by a cover.Typically, the solid core is made of polybutadiene, which is chemicallycross-linked with peroxide, or sulfur compounds together withco-cross-linking agent, such as zinc diacrylate. The cover of such ballsoften comprises tough, cut-proof blends of one or more materials knownas ionomers, which typically are ethylene/acrylic acid copolymers orethylene/acrylic acid/acrylate terpolymers in which some or all of theacid groups are neutralized with metal cations. Such ionomers arecommercially available under trademarks such as SURLYN®, which areresins sold commercially by DuPont, of Wilmington, Del., or IOTEK® whichis sold commercially by ExxonMobil, of Irving, Tex.

The combination of the above-described core and cover materials providesa “hard” covered ball that is resistant to cutting and other damagecaused by striking the ball with a golf club. Further, such acombination imparts a high initial velocity to the ball, which resultsin increased distance. Due to their hardness, however, these two-pieceballs have a relatively low spin rate, which makes them difficult tocontrol, particularly on relatively short approach shots. As such, theseballs generally are considered to be “distance” balls. Because thematerials of two-piece balls are very rigid, the balls typically have ahard “feel” when struck by a club. Softer cover materials, e.g., balataor softer ionomers or polyurethanes in some instances, have beenemployed in two-piece balls in order to provide improved “feel” andincreased spin rates, although sometimes with a reduction the ball'sspeed or C.O.R.

The C.O.R. of a one-piece golf ball is a function of it's composition.In two-piece golf balls and multi-layered golf balls, the C.O.R. is afunction of the various properties of the core, the cover, and anyadditional layer. Although the United States Golf Association (U.S.G.A.)has not promulgated any limitations on the C.O.R. values for golf balls,it has instituted a rule prohibiting the competitive use in anyU.S.G.A.-sanctioned event of a golf ball that can achieve an initialvelocity greater than 76.2 meters per second (m/s), or 250 ft/s, whenstruck by a golf club driver having a velocity of 39.6 m/s, i.e., 130ft/s (referred to hereinafter as “the U.S.G.A. test”). However, anallowed tolerance of two percent permits manufacturers to produce golfballs that achieve an initial velocity of 77.7 m/s (255 ft/s).

Regardless of the form of the golf ball, players generally seek a ballthat delivers maximum distance, which requires a high initial velocityupon impact. Therefore, in an effort to meet the demands of themarketplace, golf ball manufacturers strive to produce balls deliveringinitial velocities in the U.S.G.A. test that approximate the U.S.G.A.maximum of 77.7 m/s, or 255 ft/s, as closely as possible. Golf ballmanufacturers also generally strive to maximize the ball's C.O.R.without violating the velocity limitation. Also, to maximize distance,it is advantageous if the balls have a lower driver spin rate. Finallyit is highly desirable if, while providing increased velocity anddistance, the balls also will exhibit a soft shot feel.

Recently, several golf ball manufacturers have introduced multi-layerballs, i.e., balls having at least a core, an intermediate layer ormantle, and one or more cover layers. The goal of these manufacturershas been to overcome some of the undesirable aspects of conventionaltwo-piece balls, e.g., their hard feel. Such a multi-layer structureallows the introduction of new materials of varying hardness, wherebydeficiencies in a property in one layer can be mitigated by theintroduction of a different material in another layer. For example, tooptimize ball hardness and “feel,” blends of copolymeric high-acidionomers with softer terpolymeric ionomers have been used as a layermaterial in a golf ball but again, often with a concurrent loss ofC.O.R. and/or speed.

Numerous examples of multi-layer combinations are available. Forexample, U.S. Pat. No. 4,431,193 discloses a golf ball having amulti-layer cover, in which the inner cover layer is a relatively hard,high flexural modulus ionomer resin and the outer cover layer is arelatively soft, low flexural modulus ionomer resin.

Also, U.S. Pat. No. 6,368,237 discloses a multi-layer golf ballcomprising a core, an inner cover layer, and an outer cover layer. Theinner cover layer comprises a high-acid ionomer or ionomer blend. Theouter cover layer comprises a soft, very low-modulus ionomer or ionomerblend, or a non-ionomeric thermoplastic elastomer such as polyurethane,polyester, or polyesteramide. The resulting multi-layer golf ball issaid to provide an enhanced distance without sacrificing playability ordurability when compared to known multi-layer golf balls.

U.S. Pat. Nos. 6,416,424, 6,416,424, and 6,419,594, likewise, disclosemulti-layer golf balls comprising a core, an inner cover layer, and anouter cover layer. The inner cover layer comprises a low-acid ionomerblend. The outer cover layer comprises a soft, very low modulus ionomeror ionomer blend, or a non-ionomeric thermoplastic elastomer such aspolyurethane, polyester, or polyesteramide. The resulting multi-layergolf ball is said to provide an enhanced distance without sacrificingplayability or durability when compared to known multi-layer golf balls.

U.S. Pat. Nos. 6,503,156 and 6,506,130, likewise, disclose multi-layergolf balls comprising a core, an inner cover layer, and an outer coverlayer. The inner cover layer comprises a low-acid ionomer blend. Theouter cover layer comprises a soft, non-ionomeric thermoplastic orthermosetting elastomer such as polyurethane, polyester, orpolyesteramide. The resulting multi-layered golf ball is said to providean enhanced distance without sacrificing playability or durability whencompared to known multi-layer golf balls.

Another approach to optimizing golf ball performance has been toincorporate selected additives into the polymer compositions used tomake the various ball layers, in order to modify the polymer properties.Such additives include the metal salts of various fatty acids. Forexample, U.S. Pat. Nos. 5,312,857 and 5,306,760 disclose covercompositions for golf ball construction comprising mixtures of ionomerresins and 25-100 parts by weight of various fatty acid salts (i.e.,metal stearates, metal oleates, metal palmitates, metal pelargonates,metal laurates, etc.). However, the patents fail to disclose any majoreffects on ball properties, and fail to disclose that the compositionsare useful for parts of a golf ball other than the cover.

Recent attempts to extend the concept of the use of multi-layer coversto mitigate the harsh feel of the harder ionomer materials have alsoresulted in the development of modified ionomers for use in golf ballcompositions. For instance, U.S. Pat. No. 6,100,321 and U.S. PatentPublication No. 2003/0158312 A1 disclose ionomer compositions that aremodified with 25 to 100 parts by weight of a fatty acid salt such as ametal stearate, for producing golf balls having good resilience and highsoftness. Unlike the earlier-mentioned patents, which have employedmetal stearates as a filler material, U.S. Pat. No. 6,100,321 and U.S.Patent Publication No. 2003/0158312 A1 contemplates the use ofrelatively low levels of a stearic acid moiety, particularly metalstearates, to modify ionomers to produce improved resilience for a givenlevel of hardness or PGA Compression values. The stearate-modifiedionomers are taught as being especially useful when the ionomer isformulated for use as a golf ball core or center, as a one-piece golfball, or as a soft golf ball cover. However, there is no disclosure ofany ball construction parameters required to produce specificperformance properties such as driver velocity or driver spin forthree-piece balls.

Subsequent patents have furthered the use of such modified ionomers ingolf ball covers. For example, U.S. Pat. No. 6,329,458 discloses a golfball cover comprising an ionomer resin and a metal “soap,” e.g., calciumstearate. Finally, U.S. Pat. No. 6,616,552 discloses a golf ballincluding a multi-layer cover, one layer of which includes a heatedmixture of an ionomer resin and a metal salt of a fatty acid, e.g.,calcium stearate.

It should be appreciated from the foregoing description that thereremains a need for a golf ball that can provide maximum C.O.R. withoutviolating the velocity limitation. Also, to maximize distance, it isdesirable for such balls to have a lower driver spin rate and to exhibita soft shot feel. The present invention satisfies this need.

SUMMARY OF THE INVENTION

The present invention is embodied in a multi-piece golf ball having acore, an intermediate layer, and a cover layer, wherein the ballprovides a high driver ball speed and/or a high Coefficient ofRestitution (“C.O.R.”), while maintaining excellent shot feel. Moreparticularly, the intermediate layer of the ball comprises a modifiedionomeric polymer that comprises a special blend composition and/or aspecial bimodal polymer blend composition. The special blend compositioncomprises: (1) ethylene, (2) 5 to 25 weight percent (meth)acrylic acid(based on the total weight of (1), (2), and (3)), (3) 0 to 40 weightpercent of a C₁ to C₈— alkyl acrylate (based on the total weight of (1),(2), and (3)), and (4) about 5 to about 45 weight percent (based on thetotal weight of the modified ionomeric polymer), of a fatty acid or oneor more metal salts of the fatty acid. The special bimodal polymer blendcomposition comprises (1) a high molecular weight component havingmolecular weight of about 80,000 to about 500,000 and comprising one ormore ethylene/α, β-ethylenically unsaturated C₃₋₈ carboxylic acidcopolymers and/or one or more ethylene/alkyl(meth)acrylate/(meth)acrylicacid terpolymers; the high molecular weight component being partiallyneutralized with metal ions selected from the group consisting oflithium, sodium, zinc, calcium, magnesium, and a mixture of any these,and/or (2) a low molecular weight component having a molecular weight ofabout from about 2,000 to about 30,000 and comprising one or moreethylene/α, β-ethylenically unsaturated C₃₋₈ carboxylic acid copolymersand/or one or more ethylene, alkyl(meth)acrylate, (meth)acrylic acidterpolymers; the low molecular weight component being partiallyneutralized with metal ions selected from the group consisting oflithium, sodium, zinc, calcium, magnesium, and a mixture of any these,and (3) about 5 to about 45 weight percent (based on the total weight ofthe modified ionomeric polymer) of a fatty acid or one or more metalsalts of the fatty acid. At least about 40 percent of the acid groupspresent in the modified ionomeric polymer are neutralized with zinc,sodium, lithium, calcium, or magnesium ions, or a combination thereof.

In addition, the core has a diameter in the range of preferably about1.20 to about 1.56 in., more preferably about 1.40 to about 1.52 in.,and most preferably about 1.45 to about 1.50 in. The core also has a PGAcompression in the range of preferably about 40 to about 90, morepreferably about 40 to about 85, and most preferably about 40 to about80.

The intermediate layer has a thickness in the range of preferably about0.01 to about 0.10 in., more preferably about 0.02 to about 0.08 in.,and most preferably about 0.03 to about 0.06 in. The intermediate layerhas a Shore D hardness in the range of preferably about 30 to about 75,more preferably about 40 to about 70, and most preferably about 40 toabout 65. The modified ionomeric polymer present in the intermediatelayer comprises preferably about 7 to about 35 weight percent, and morepreferably about 8 to about 20 weight percent, (based on the totalweight of the modified ionomeric polymer) of one or more metal fattyacids or metal salts of a fatty acid, wherein the metal is selected fromthe group consisting of calcium, sodium, zinc, lithium, magnesium,barium, and combinations thereof. Preferably about 50 to 100 percent,and more preferably about 70 to 100 percent, of the acid groups presentin the modified ionomeric polymer present in the intermediate layer areneutralized with zinc, sodium, lithium, calcium, or magnesium ions, or acombination thereof. The preferred average acid content is in the rangeof about 5 to about 25 weight percent.

The cover layer has a Shore D hardness in the range of preferably about40 to about 70, more preferably about 45 to about 70, and mostpreferably about 50 to about 70.

In other more detailed features of the invention, the modified ionomericpolymer of the intermediate layer further comprises a zinc-neutralizedionomer of a polymer having the general formula E/X/Y, where E isethylene, X is an alkyl(meth)acrylate present in an amount in the rangeof 0 to about 50 weight percent (based on the total weight of thezinc-neutralized ionomer), and Y is (meth)acrylic acid present in anamount in the range of about 5 to about 25 weight percent (based on thetotal weight of the zinc-neutralized ionomer).

In yet another more detailed feature of the invention, the core furthercomprises (1) at least one unsaturated polymer, (2) at least onecross-linking agent, and (3) at least one co-cross-linking agent. Theunsaturated polymer has a Mooney viscosity (ML₁₊₄ (100° C.)) in therange of about 20 to about 80 and is selected from the group consistingof 1,2-polybutadiene, cis-1,4-polybutadiene, trans-1,4-polybutadiene,cis-polyisoprene, trans-polyisoprene, polychloroprene, polybutylene,styrene-butadiene rubber, styrene-butadiene-styrene block copolymer andpartially and fully hydrogenated equivalents, styrene-isoprene-styreneblock copolymer and partially and fully hydrogenated equivalents,nitrile rubber, silicone rubber, polyurethane, any combinations thereof.In addition, the cross-linking agent is present in an amount in therange of about 0.05 to about 5 parts by weight of the cross-linkingagents per 100 parts by weight of the unsaturated polymer.

Further, the core can optionally comprise a peptizer, an accelerator,and/or a filler. The optional peptizer can comprise an organic sulfurcompound, a metal salt of an organic sulfur compound, and/or a non-metalsalt of an organic sulfur compound. The optional accelerator can bepresent in an amount in the range of about 0.1 to about 10 parts byweight per 100 parts by weight of the unsaturated polymer. The optionalfiller is selected from the group consisting of precipitated hydratedsilica, limestone, clay, talc, asbestos, barytes, glass fibers, aramidfibers, mica, calcium metasilicate, barium sulfate, zinc sulfide,lithopone, silicates, silicon carbide, diatomaceous earth, carbonatessuch as calcium or magnesium or barium carbonate, sulfates such ascalcium or magnesium or barium sulfate, metals, including tungsten steelcopper, cobalt or iron, metal alloys, tungsten carbide, metal oxides,metal stearates, other particulate carbonaceous materials, andcombinations thereof.

In yet other more detailed features of the invention, the unsaturatedpolymer is cis-1,4-polybutadiene and has a Mooney viscosity (ML₁₊₄ (100°C.)) in the range of about 30 to about 70, and the cross-linking agentis present in an amount in the range of about 0.2 to about 3 parts byweight per 100 parts by weight of the unsaturated polymer. The optionalpeptizer comprises an organic sulfur compound or metal salt of anorganic sulfur compound, or a non-metal salt of an organic sulfurcompound, present in an amount in the range of about 0.01 to about 10parts by weight per 100 parts by weight of the unsaturated polymer. Alsoin this case, the optional accelerator is present in an amount in therange of about 0.2 to about 5 parts by weight per 100 parts by weight ofthe unsaturated polymer.

More particularly, the unsaturated polymer is cis-1,4-polybutadiene andhas a Mooney viscosity (ML₁₊₄ (100° C.)) in the range of about 35 toabout 50, and the cross-linking agent is present in an amount in therange of about 0.2 to about 2 parts by weight per 100 parts by weight ofthe unsaturated polymer. In this case, the optional peptizer comprisespentachlorothiophenol, dibenzamido diphenyldisulfide, a metal salt ofpentachloro-thiophenol, or an ammonium salt of pentachlorothiophenol, ora combination thereof, present in an amount in the range of about 0.1 toabout 7 parts by weight per 100 parts by weight of the unsaturatedpolymer. Preferably, the peptizer is the NH₄ ⁺ salt ofpentachlorothiophenol, present in amount in the range of about 0.15 toabout 5 parts by weight per 100 parts by weight of the unsaturatedpolymer. Also in this case, the optional accelerator is present in anamount in the range of about 0.5 to about 1.5 parts by weight per 100parts by weight of the unsaturated polymer, and wherein the acceleratoris selected from the group consisting of 2-mercaptobenzothiazole and asalt of 2-mercaptobenzothiazole.

The core preferably comprises a first cross-linking agent having a firstcharacteristic decomposition temperature less than 150° C. for a t_(1/2)equal to 0.1 hour, and a second cross-linking agent having a secondcharacteristic decomposition temperature greater than 150° C. for at_(1/2) equal to 0.1 hour. The composition weight ratio of the firstcross-linking agent to the second cross-linking agent is in the range ofpreferably 5:95 to 95:5, and more preferably 10:90 to 50:50.

The golf ball of the invention preferably has a coefficient ofrestitution greater than about 0.790, at 125 ft/sec inbound velocity. Inaddition, one or more of the core, the intermediate layer, and the coverlayer preferably further comprises a polymer selected from the groupconsisting of thermoplastic elastomers, thermoset elastomers, syntheticrubber, thermoplastic vulcanizates, polycarbonate, polyolefin,polyamide, copolymeric polyamide, polyesters, polyvinyl alcohols,acrylonitrile-butadiene-styrene copolymers, polyarylate, polyacrylate,polyphenylene ether, impact-modified polyphenylene ether, high impactpolystyrene, diallyl phthalate polymer, metallocene catalyzed polymers,styrene-acrylonitrile (SAN) (including olefin-modified SAN andacrylonitrile-styrene-acrylonitrile), styrene-maleic anhydride (S/MA)polymer, styrenic copolymer, functionalized styrenic copolymer,functionalized styrenic terpolymer, styrenic terpolymer, cellulosepolymer, liquid crystal polymer (LCP), ethylene-propylene-dieneterpolymer (EPDM), ethylene-vinyl acetate copolymers (EVA),ethylene-propylene copolymer, ethylene vinyl acetate, polyurea, andpolysiloxane, or any metallocene-catalyzed polymers of these species.

The core can comprise a center and one or more core layers disposedaround such center. The difference between the hardnesses of one corelayer and the next adjacent core layer is preferably greater than 2Shore D units. This hardness difference can increase outwards, from thecenter to the outermost core layer. Alternatively, this hardnessdifference can decrease outwards, from the center to the outermost corelayer. The difference between the specific gravity of one core layer andthe next adjacent layer preferably is greater than 0.1, and morepreferably is greater than 0.2. This specific gravity difference canincrease outwards, from the center to the outermost core layer.Alternatively, this specific gravity difference can decrease outwards,from the center to the outermost core layer.

The cover layer can comprise an ionomeric polymer comprising one or moreE/X/Y copolymers, wherein E is ethylene, X is a C₃ to C₈ α,βethylenically unsaturated carboxylic acid, and Y is a softeningcomonomer selected from the group consisting of alkyl acrylate and alkylmethacrylate, wherein the alkyl groups have from 1 to 8 carbon atoms, orionomers of such E/X/Y copolymers, wherein X is in the range of about 5to about 35 weight % of the E/X/Y copolymer and Y is in the range of 0to about 50 weight % of the E/X/Y copolymer, and wherein the acid groupspresent in said ionomeric polymer are partially neutralized with a metalselected from the group consisting of zinc, sodium, lithium, calcium,magnesium, and combinations thereof. Alternatively, the cover layer maycomprise a bimodal ionomeric polymer comprising a high molecular weightcomponent having a molecular weight in the range of about 80,000 toabout 500,000 and comprising one or more ethylene/α,β-ethylenicallyunsaturated C₃₋₈ carboxylic acid copolymers and/or one or moreethylene/alkyl(meth)acrylate/(meth)acrylic acid terpolymers, wherein thehigh molecular weight component is partially neutralized with metal ionsselected from the group consisting of lithium, sodium, zinc, calcium,magnesium, and combinations thereof, and a low molecular weightcomponent having a molecular weight in the range of about 2,000 to about30,000 and comprising one or more ethylene/α,β-ethylenically unsaturatedC₃₋₈ carboxylic acid copolymers and/or one or moreethylene/alkyl(meth)acrylate/(meth)acrylic acid terpolymers, whereinsaid low molecular weight component is partially neutralized with metalions selected from the group consisting of lithium, sodium, zinc,calcium, magnesium. The cover layer may also comprise a mixture of anionomeric polymer and a bimodal ionomeric polymer.

In other more detailed features of the invention, the cover layer inaddition to an ionomeric or bimodal ionomeric polymer may furthercomprise a zinc-neutralized ionomer of a polymer having the generalformula E/X/Y, where E is ethylene, X is an alkyl(meth)acrylate presentin an amount in the range of 0 to about 50 weight percent (based on thetotal weight of the zinc-neutralized ionomer), and Y is (meth)acrylicacid present in an amount in the range of about 5 to about 25 weightpercent (based on the total weight of the zinc-neutralized ionomer).

Other features and advantages of the present invention should becomeapparent from the following description of the preferred embodiment,taken in conjunction with the accompanying drawings, which illustrates,by way of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE is a cross-sectional view of a golf ball embodying theinvention, illustrating the ball's core, intermediate layer, and coverlayer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Any numerical values recited herein include all values from the lowervalue to the upper value in increments of one unit, provided that thereis a separation of at least 2 units between any lower value and anyhigher value. As an example, if it is specified that the amount of acomponent or a value of a process variable preferably is from 1 to 90,more preferably from 20 to 80, and most preferably from 30 to 70, it isintended that values such as 15 to 85, 22 to 68, 43 to 51, 30 to 32 etc.are expressly included in this specification. For values having lessthan one unit difference, one unit is considered to be 0.1, 0.01, 0.001,or 0.0001, as appropriate. Thus all possible combinations of numericalvalues between the lowest value and the highest value enumerated hereinshould be considered to be expressly stated in this application.

The term “(meth)acrylic acid copolymers” is intended to mean copolymersof methacrylic acid and/or acrylic acid.

The term “(meth)acrylate” is intended to mean an ester of methacrylicacid and/or acrylic acid.

The term “partially neutralized” is intended to mean an ionomer having adegree of neutralization of less than 100 percent.

The term “hydrocarbyl” is intended to mean any aliphatic,cycloaliphatic, aromatic, aryl-substituted aliphatic, aryl-substitutedcycloaliphatic, aliphatic-substituted aromatic, orcycloaliphatic-substituted aromatic groups. The aliphatic orcycloaliphatic groups are preferably saturated. Likewise, the term“hydrocarbyloxy” is intended to mean a hydrocarbyl group having anoxygen linkage between it and the carbon atom to which it is attached.

The term “outer cover layer” is used interchangeably with the term“cover layer” and is intended to mean the outermost layer of a golfball.

The term “core” is intended to mean the elastic center of the golf ball.The core may have one or more layers of elastic material, which areusually made of rubbery material such as diene rubbers.

The term “cover layer” is intended to mean the outermost layer of thegolf ball, which is the layer that is directly in contact with paintand/or ink on the ball's outer surface. If the cover includes two ormore layers, only the outermost layer is designated the cover layer andthe remaining layers (excluding the outermost layer) are commonlydesignated intermediate layers as herein defined.

The term “intermediate layer” is used interchangeably with the term“mantle layer” or “inner cover layer,” and it is intended to refer toany layer(s) in a golf ball disposed between the core and the coverlayer. With respect to the optimization of the thickness and hardness ofthe intermediate layer defined herein, when a plurality of inner layersare included, the thickness and hardness of all the inner layerscombined are referred to.

Golf Ball Core

Referring to now to the FIGURE, there is illustrated a golf ball 10 thatincludes a solid center or core 12, formed as a solid, spherical body ofthe formulation described below. This core comprises the followingcomponents:

a) Unsaturated Polymer

The core 12 of the golf ball 10 of the present invention comprises anunsaturated polymer. Unsaturated polymers suitable for use in the golfballs of the present invention include any polymeric material having anunsaturation, either hydrocarbon or non-hydrocarbon, capable ofparticipating in a cross-linking reaction initiated thermally,chemically, by irradiation, or by a combination of these methods. Theunsaturated polymer can be any rubber commonly used in conventionalone-piece golf balls and the cores of multi-layered golf balls.Non-limiting examples of suitable unsaturated polymers include1,2-polybutadiene, cis-1,4-polybutadiene, trans-1,4-polybutadiene,cis-polyisoprene, trans-polyisoprene, polychloroprene, polybutylene,styrene-butadiene rubber, styrene-butadiene-styrene block copolymer andpartially and fully hydrogenated equivalents, styrene-isoprene-styreneblock copolymer and partially and fully hydrogenated equivalents,nitrile rubber, silicone rubber, and polyurethane, as well as mixturesof these.

Polybutadiene rubbers, especially 1,4-polybutadiene rubbers containingat least 40 mol %, and more preferably 80 to 100 mol % of cis-1,4 bonds,are preferred, because of their high rebound resilience, moldability,and high strength after vulcanization. The polybutadiene component maybe synthesized using rare earth-based catalysts, nickel-based catalysts,or cobalt-based catalysts, as conventionally used in this field.

Polybutadiene obtained using lanthanum rare earth-based catalysts isusually synthesized by polymerizing butadiene in the presence of acatalyst comprising a combination of a lanthanum rare earth compound, anorganic aluminum compound, a Lewis base and, when necessary, a Lewisacid. The lanthanum rare earth compound may be a compound containing arare earth atom (atomic number of 57 to 71), but particularly preferredis a neodymium compound.

Examples of the nickel-based catalysts include one-component types suchas nickel diatomaceous earth, two-component types such asRaney-nickel/titanium tetrachloride, and three-component types such as anickel compound/organic metal/boron trifluoride etherate. Examples ofnickel compounds include reduced nickel with carrier, Raney-nickel,nickel oxide, nickel carboxylate, and a complex salt of organic nickel.Examples of the organic metals include a trialkyl aluminum such astriethyl aluminum, tri-n-propyl aluminum, tri-isobutyl aluminum, ortri-n-hexyl aluminum; an alkyl lithium such as n-butyl lithium,sec-butyl lithium, tert-butyl lithium, or 1,4-dibutane lithium; and adialkyl zinc such as diethyl zinc or dibutyl zinc.

Examples of the cobalt-based catalysts include, as cobalt and compoundsthereof, Raney-cobalt, cobalt chloride, cobalt bromide, cobalt iodide,cobalt oxide, cobalt sulfate, cobalt carbonate, cobalt phosphate, cobaltphthalate, cobalt carbonyl, cobalt acetylacetonate, cobalt diethyldithiocarbamate, cobalt anilinium nitrite, and cobalt dinitrosylchloride. In particular, each of these compounds is preferably combinedwith a dialkyl aluminum monochloride such as diethyl aluminummonochloride or diisobutyl aluminum monochloride, a trialkyl aluminumsuch as triethyl aluminum, tri-n-propyl aluminum, triisobutyl aluminumor tri-n-hexyl aluminum, an aluminum alkyl sesquichloride such as ethylaluminum sesquichloride, or aluminum chloride.

The 1,4-polybutadiene rubbers have a molecular weight distribution(Mw/Mn) preferably in the range of about 1.2 to about 4.0, morepreferably about 1.7 to about 3.7, even more preferably about 2.0 toabout 3.5, and most preferably from about 2.2 to about 3.2.

The polybutadiene rubbers have a Mooney viscosity (ML1+4 (100° C.)) inthe range of preferably about 20 to about 80, more preferably about 30to about 70, even more preferably about 35 to about 60, and mostpreferably about 35 to about 50.

The term “Mooney viscosity” used herein is intended to refer to anindustrial index of viscosity, as measured by a Mooney viscometer, whichis a type of rotary plastometer (see JIS K6300). This value isrepresented by the symbol ML1+4 (100° C.), wherein “M” represents Mooneyviscosity, “L” represents large rotor (L-type), “1+4” represents apre-heating time of 1 minute and a rotor rotation time of 4 minutes, and“100° C.” indicates that measurement was carried out at a temperature of100° C.

The 1,4-polybutadiene rubbers may also be blended with natural rubber,polyisoprene rubber, styrene-butadiene rubber, or the like. At least 80%by weight of 1,4-polybutadiene rubber should be present in the baserubber, because base rubbers containing less 1,4-polybutadiene rubberoften fail to take advantage of the rebound resilience of thepolybutadiene rubber.

Many different types of 1,2 polybutadienes exist, having widely varyingphysical properties as a result of their differing tacticity,crystallinity, and molecular weight. Examples of 1,2 polybutadieneshaving differing tacticity, all of which are suitable as unsaturatedpolymers for use in the present invention, are atactic 1,2polybutadiene, isotactic 1,2 polybutadiene, and syndiotactic 1,2polybutadiene. Syndiotactic polymers include alternating base units thatare enantiomers of each other. These 1,2 polybutadienes are alsodifferentiated by their crystallinity, which ranges from amorphous 1,2polybutadienes that essentially lack crystallinity to semi crystalline1,2 polybutadienes of varying crystallinities. The molecular weights ofthese 1,2-polybutadienes can also vary greatly. The various combinationsof tacticity, crystallinity, and molecular weight provide for manydifferent types of 1,2 polybutadienes having very differentprocessability, as well as other chemical, thermal, mechanical, andrheological properties. Syndiotactic 1,2-polybutadiene having acrystallinity suitable for use as an unsaturated polymer in compositionswithin the scope of the present invention are polymerized from a 1,2addition of butadiene. Golf balls within the scope of the presentinvention include syndiotactic 1,2-polybutadiene having crystallinityand greater than about 70% of 1,2 bonds, more preferably greater thanabout 80% of 1,2-bonds, and most preferably greater than about 90% of1,2-bonds. Also, golf balls within the scope of the present inventionmay include syndiotactic 1,2-polybutadiene having a crystallinitybetween about 5% and about 50%, more preferably between about 10% andabout 40%, and most preferably between about 15% and about 30%. Inaddition, golf balls within the scope of the present invention mayinclude syndiotactic 1,2-polybutadiene having crystallinity and a meanmolecular weight between about 10,000 and about 350,000, more preferablybetween about 50,000 and about 300,000, more preferably between about80,000 and about 200,000, and most preferably between about 10,000 andabout 150,000. Examples of suitable syndiotactic 1,2-polybutadieneshaving crystallinity suitable for use in golf balls within the scope ofthe present invention are sold under the trade names RB810, RB820, andRB830 by JSR Corporation of Tokyo, Japan. These have more than 90% of1,2 bonds, a mean molecular weight of approximately 120,000, and acrystallinity between about 15% and about 30%.

In one embodiment of the invention, the core 12 may comprise a centerand one or more core layers disposed around the center. These corelayers may be made from the same rubber as is used in the centerportion, or they may be a different thermoplastic elastomer. The variouscore layers (including the center) may each exhibit a differenthardness. The Shore D hardness difference between the center hardnessand that of the next adjacent layer, as well as the difference inhardness between the various core layers preferably is greater than 2,more preferably is greater than 5, and most preferably is greater than10 units.

In one preferred embodiment, the hardness of the center and eachsequential layer increases progressively outwards from the center toouter core layer.

In another preferred embodiment, the hardness of the center and eachsequential layer decreases progressively outwards from the center to theouter core layer.

In one embodiment of the invention, the core 12 may comprise a centerand one or more core layers disposed around the center. These corelayers may be made from the same rubber as is used in the center, orthey may be made from a different thermoplastic elastomer. The variouscore layers (including the center) may each exhibit a different specificgravity. The specific gravity difference between the center and that ofthe next adjacent layer, as well as the difference in specific gravitybetween adjacent ones of the various core layers, preferably is greaterthan 0.1, and more preferably is greater than 0.2.

In one preferred embodiment, the specific gravity of the center and eachsequential layer increases progressively outwards from the center toouter core layer.

In another preferred embodiment, the specific gravity of the center andeach sequential layer decreases progressively outwards from the centerto the outer core layer.

b) Cross-Linking Agents

Suitable cross-linking agents for use in the golf balls of the presentinvention include peroxides, sulfur compounds, or other known chemicalcross-linking agents, as well as mixtures of these. Non-limitingexamples of suitable cross-linking agents include primary, secondary, ortertiary aliphatic or aromatic organic peroxides. Peroxides containingmore than one peroxy group can be used, such as2,5-dimethyl-2,5-di(tert-butylperoxy)hexane and 1,4-di-(2-tert-butylperoxyisopropyl)benzene. Both symmetrical and asymmetrical peroxides canbe used, for example, tert-butyl perbenzoate and tert-butyl cumylperoxide. Peroxides incorporating carboxyl groups also are suitable. Thedecomposition of peroxides used as cross-linking agents in the presentinvention can be brought about by applying thermal energy, shear,irradiation, reaction with other chemicals, or any combination of these.Both homolytically and heterolytically decomposed peroxide can be usedin the present invention. Non-limiting examples of suitable peroxidesinclude: diacetyl peroxide; di-tert-butyl peroxide; dibenzoyl peroxide;dicumyl peroxide; 2,5-dimethyl-2,5-di(benzoylperoxy)hexane;1,4-bis-(t-butylperoxyisopropyl)benzene; t-butylperoxybenzoate;2,5-dimethyl-2,5-di-(t-butylperoxy)hexyne-3, such as Trigonox 145-45B,marketed by Akrochem Corp. of Akron, Ohio; 1,1-bis(t-butylperoxy)-3,3,5tri-methylcyclohexane, such as Varox 231-XL, marketed by R.T. VanderbiltCo., Inc. of Norwalk, Conn.; and di-(2,4-dichlorobenzoyl)peroxide. Thecross-linking agents can be blended in total amounts of about 0.05 partto about 5 parts, more preferably about 0.2 part to about 3 parts, andmost preferably about 0.2 part to about 2 parts, by weight of thecross-linking agents per 100 parts by weight of the unsaturated polymer.

Each cross-linking agent has a characteristic decomposition temperatureat which 50% of the cross-linking agent has decomposed when subjected tothat temperature for a specified time period (t1/2). For example,1,1-bis-(t-butylperoxy)-3,3,5-tri-methylcyclohexane at t1/2=0.1 hr has adecomposition temperature of 138° C. and2,5-dimethyl-2,5-di-(t-butylperoxy)hexyne-3 at t1/2=0.1 hr has adecomposition temperature of 182° C. Two or more cross-linking agentshaving different characteristic decomposition temperatures at the samet1/2 may be blended in the composition. For example, where at least onecross-linking agent has a first characteristic decomposition temperatureless than 150° C., and at least one cross-linking agent has a secondcharacteristic decomposition temperature greater than 150° C., thecomposition weight ratio of the first one cross-linking agent to thesecond cross-linking agent preferably is in range from 5:95 to 95:5, andmore preferably in the range of 10:90 to 50:50.

Besides the use of chemical cross-linking agents, exposure of thecomposition to radiation also can serve as a cross-linking agent.Radiation can be applied to the unsaturated polymer mixture by any knownmethod, including using microwave or gamma radiation, or an electronbeam device. Additives may also be used to improve radiation curing ofthe diene polymer.

c) Co-Cross-Linking Agent

The rubber and cross-linking agent may be blended with aco-cross-linking agent, which may be a metal salt of an unsaturatedcarboxylic acid. Examples of such metal salts include zinc and magnesiumsalts of unsaturated fatty acids having 3 to 8 carbon atoms, such asacrylic acid, methacrylic acid, maleic acid, fumaric acid, and palmiticacid, with the zinc salts of acrylic and methacrylic acid being mostpreferred. The unsaturated carboxylic acid metal salt can be blended ina rubber either as a preformed metal salt, or by introducing anα,β-unsaturated carboxylic acid and a metal oxide or hydroxide into therubber composition, and allowing them to react in the rubber compositionto form a metal salt. The unsaturated carboxylic acid metal salt can beblended in any desired amount, but preferably in amounts of about 10parts to about 60 parts by weight of the unsaturated carboxylic acid per100 parts by weight of the unsaturated polymer.

d) Peptizer

The compositions used to formulate the cores of the balls of the presentinvention may also incorporate one or more peptizers. The term“peptizer” is intended to mean chemicals that inhibit cross-linkingduring the initial processing of unsaturated polymers, but thenparticipate in the cross-linking of the unsaturated polymer aftercross-linking has commenced.

The peptizer preferably comprises an organic sulfur compound and/or itsmetal or non-metal salt. Examples of such organic sulfur compoundsinclude thiophenols, such as pentachlorothiophenol,4-butyl-o-thiocresol, 4 t-butyl-p-thiocresol, and 2-benzamidothiophenol;thiocarboxylic acids, such as thiobenzoic acid; 4,4′ dithiodimorpholine; and, sulfides, such as dixylyl disulfide, dibenzoyldisulfide; dibenzothiazyl disulfide; di(pentachlorophenyl)disulfide;dibenzamido diphenyldisulfide (DBDD), and alkylated phenol sulfides,such as VULTAC marketed by Atofina Chemicals, Inc. of Philadelphia, Pa.Preferred organic sulfur compounds include pentachlorothiophenol anddibenzamido diphenyldisulfide.

Examples of the metal salt of an organic sulfur compound include sodium,potassium, lithium, magnesium, calcium, barium, cesium, and zinc saltsof the above-mentioned thiophenols and thiocarboxylic acids, with thezinc salt of pentachlorothiophenol being most preferred.

Examples of the non-metal salt of an organic sulfur compound includeammonium salts of the above-mentioned thiophenols and thiocarboxylicacids, wherein the ammonium cation has the general formula [NR¹R²R³R⁴]⁺,where R¹, R², R³′ and R⁴ is either hydrogen, or a C₁-C₂₀ aliphatic,cycloaliphatic or aromatic moiety, or any and all combinations thereof,with the most preferred being the NH₄ ⁺-salt Of pentachlorothiophenol.

When the peptizer employed in the cores of the golf balls of the presentinvention is an organic sulfur compound or a metal salt of an organicsulfur compound, or a non-metal salt of an organic sulfur compound, itis employed in an amount in the range of preferably about 0.01 to about10, more preferably about 0.10 to about 7, and most preferably about0.15 to about 5, parts by weight per 100 parts by weight of theunsaturated polymer component.

e) Accelerators

The golf ball composition can comprise one or more accelerators of oneor more classes. Accelerators added to an unsaturated polymer increasethe vulcanization rate and/or decrease the vulcanization temperature ofthe unsaturated polymers. Accelerators can be of any class known forrubber processing including mercapto-, sulfenamide-, thiuram,dithiocarbamate, dithiocarbamylsulfenamide, xanthate, guanidine, amine,thiourea, and dithiophosphate accelerators. Specific commercialaccelerators include 2-mercaptobenzothiazole and its metal or non-metalsalts, such as Vulkacit Mercapto C, Mercapto MGC, Mercapto ZM-5, and ZMmarketed by Bayer AG of Leverkusen, Germany, Nocceler M, Nocceler MZ,and Nocceler M-60 marketed by Ouchisinko Chemical Industrial Company,Ltd. of Tokyo, Japan, and MBT and ZMBT marketed by Akrochem Corporationof Akron, Ohio. A more complete list of commercially availableaccelerators is given in The Vanderbilt Rubber Handbook: 13th Edition(1990, R.T. Vanderbilt Co.), pp. 296-330, in Encyclopedia of PolymerScience and Technology, Vol. 12 (1970, John Wiley & Sons), pp. 258-259,and in Rubber Technology Handbook (1980, Hanser/Gardner Publications),pp. 234-236. Preferred accelerators include 2-mercaptobenzothiazole(MBT) and its salts.

The ball composition can further incorporate in the range of about 0.1part to about 10 parts by weight of the accelerator per 100 parts byweight of the unsaturated polymer. More preferably, the ball compositioncan further incorporate about 0.2 part to about 5 parts, and mostpreferably from about 0.5 part to about 1.5 parts, by weight of theaccelerator per 100 parts by weight of the unsaturated polymer

Golf balls within the scope of the present invention can be prepared bymolding the rubber composition as formulated above into a core ofdesired size and vulcanizing the rubber by heating. The manufacture ofthese spheres can be in accord with conventional methods and conditionsof manufacture. After the cores have been made, the various inner andouter cover layers are then formed over them.

Cover Layer

With reference again to the FIGURE, the intermediate layer 14 of thegolf ball 10 is disposed over the core 12 and an outer cover layer 16 isdisposed over the intermediate layer. The composition of the outer coverlayer comprises the following components.

The cover layer 16 can comprise one or more ionomer resins or blendsthereof. Methods for preparing such ionomers are well known in the art,for example as disclosed in U.S. Pat. No. 3,264,272, the entire contentsof which are herein incorporated by reference. Ionomerresins have beenlong utilized in golf ball formulations and have, to a large extent,replaced balata as the standard golf ball cover stock material.Generally speaking, commercial ionomers consist of a polymer of amono-olefin, e.g., an alkene, with an unsaturated mono- or dicarboxylicacids having 3 to 12 carbon atoms. An additional monomer in the form ofa mono- or dicarboxylic acid ester also may be incorporated in theformulation as a so-called “softening comonomer.”

The incorporated carboxylic acid groups are then neutralized by a basicmetal ion salt, to form the ionomer. The metal cations of the basicmetal ion salt used for neutralization include Li⁺, Na⁺, K⁺, Zn²⁺, Co²⁺,Ni²⁺, Cu²⁺, Pb²⁺, and Mg²⁺, with Li+, Na+, Zn²⁺, and Mg²⁺ beingpreferred. The basic metal ion salts include, for example, formic acid,acetic acid, nitric acid, carbonic acid, hydrogen carbonate salts,oxides, hydroxides, and alkoxides.

The first commercially available ionomer resins contained up to 16weight percent acrylic or methacrylic acid, although even at that time,it was well known that, as a general rule, the hardness of these covermaterials could be increased with increasing acid content. Thus, inResearch Disclosure 29703, published in January, 1989, first disclosedionomers based on ethylene/acrylic acid or ethylene/methacrylic acidcontaining acid contents of greater than 15 weight percent. In this samedisclosure, DuPont also taught that such so called “high acid ionomers”had significantly improved stiffness and hardness and thus could beadvantageously used in golf ball construction, when used either singlyor in a blend with other ionomers.

More recently, high-acid ionomers are typically defined as those ionomerresins with acrylic or methacrylic acid units present from 16 wt. % toabout 35 wt. % in the polymer. Generally, such high-acid ionomers have aflexural modulus from about 50,000 psi to about 125,000 psi.

Ionomer resins can further comprise a softening comonomer, which istypically present from about 10 wt. % to about 50 wt. % in the polymer.Such ionomers will have a flexural modulus from about 2,000 psi to about10,000 psi, and are sometimes referred to as “soft” or “very lowmodulus” ionomers. Typical softening comonomers include n-butylacrylate, iso-butyl acrylate, n-butyl methacrylate, methyl acrylate, andmethyl methacrylate.

Today, there are a wide variety of commercially available ionomer resinsbased both on copolymers of ethylene and (meth)acrylic acid orterpolymers of ethylene and (meth)acrylic acid and (meth)acrylate, allof which may be used as a component of the balls of the presentinvention. The properties of these ionomer resins can vary widely due tovariations in acid content, softening comonomer content, the degree ofneutralization, and the type of metal ion used in the neutralization.The full range commercially available typically includes ionomers ofpolymers of general formula, E/X/Y, where E is ethylene, X is anethylene/α, β-ethylenically unsaturated C₃₋₈ carboxylic acid copolymersuch as ethylene/acrylic or ethylene/methacrylic acid and is present inan amount from about 5 wt. % to about 35 wt. % of the polymer, and Y isa softening comonomer such as C₁-C₈ acrylate or methacrylate present inan amount of from 0 wt. % to about 50 wt. % of the polymer, and whereinthe acid moiety is neutralized from about 1% to about 90%, to form anionomer with a cation such as lithium, sodium, potassium, magnesium,calcium, barium, lead, tin, zinc or aluminum, or a combination of suchcations.

Other examples of ionomers for use as the cover layer of the golf ballsof the present invention are ionomers based on the so-called bimodalionomers, as described in U.S. Pat. No. 6,562,906, the entire contentsof which are herein incorporated by reference. These ionomers arebimodal, because they are prepared from blends comprising polymers ofdifferent molecular weights. Specifically, they include bimodal polymerblend compositions comprising the following:

-   -   a) a high molecular weight component having a molecular weight        of about 80,000 to about 500,000 and comprising one or more        ethylene/α, β-ethylenically unsaturated C₃₋₈ carboxylic acid        copolymers and/or one or more ethylene, alkyl(meth)acrylate,        (meth)acrylic acid terpolymers; wherein the high molecular        weight component is partially neutralized with metal ions        selected from the group consisting of lithium, sodium, zinc,        calcium, magnesium, and mixtures of any these; and    -   b) a low molecular weight component having a molecular weight of        about from about 2,000 to about 30,000 and comprising one or        more ethylene/α, β-ethylenically unsaturated C₃₋₈ carboxylic        acid copolymers and/or one or more ethylene,        alkyl(meth)acrylate, (meth)acrylic acid terpolymers; wherein the        low molecular weight component is partially neutralized with        metal ions selected from the group consisting of lithium,        sodium, zinc, calcium, magnesium, and mixtures of any these.

The cover layer may also comprise one of more of the modified ionomericpolymers, described herein for use in the intermediate layer of the golfballs of the present invention.

It is also understood that the cover layer may also comprise any and allblend combinations of the aforementioned ionomers and/or modifiedionomers.

A preferred blend combination for use as the cover layer in the golfballs of the present invention is a blend of the ionomers, bimodalionomers, or modified ionomeric polymers as described herein, furtherblended with a zinc neutralized ionomer of a polymer of general formulaE/X/Y where E is ethylene, X is a softening comonomer such as an alkylacrylate or methacrylate and is present in an amount in the range ofpreferably 0 to about 50, more preferably 0 to about 25, and mostpreferably 0, and Y is acrylic or methacrylic acid and is present in anamount in the range of preferably about 5 wt. % to about 25, morepreferably about 10 to about 25, and most preferably about 10 to about20 wt %.

In addition, the material used to prepare the outer cover layer(s) ofthe golf ball of the present invention is not limited to ionomer resins.Other possible materials for use in the cover layer(s) include otherthermoplastic resins, thermoset resins, polyurethane resins, polyesterresins, polyamide elastomer resins, polyamide-ionomer, polyurethaneionomer, thermoplastic copolyetherester block copolymer, thermoplasticcopolyesterester block copolymer, thermoplastic polyurethane, thermosetpolyurethane, dynamically vulcanized thermoplastic elastomer,styrene-butadiene, styrene-isoprene and styrene-isoprene elastomers witha functional group such as maleic anhydride or sulfonic acid, andthermoplastic or thermoset metallocene-catalyzed polyolefin resins, andany and all combinations thereof.

Intermediate Layer(s)

With reference again to the FIGURE, the intermediate layer 14 isdisposed between the core 12 and the outer cover layer 16. Theintermediate layers comprises preferably the following components:

The one or more intermediate layers 14 comprise one or more so-called“modified ionomers,” examples of which are described in U.S. Pat. Nos.6,100,321, 6,329,458, and 6,616,552, and US. Patent Publication US2003/0158312 A1, the entire contents of all of which are hereinincorporated by reference.

Specifically, at least one of the intermediate layers 14 of the golfballs 10 of the present invention comprise one or more modifiedionomeric polymers prepared by mixing

-   -   a) an ionomeric polymer comprising ethylene, 5 to 25 weight        percent (meth)acrylic acid, and 0 to 40 weight percent of a        C₁-C₈ (meth)acrylate monomer, wherein the ionomeric polymer is        neutralized with metal ions selected from the group consisting        of lithium, sodium, zinc, calcium, magnesium, and a mixture of        any these, and    -   b) one or more fatty acids or metal salts of a fatty acid,        wherein the metal is selected from the group consisting of        calcium, sodium, zinc, lithium, barium, and magnesium, and        wherein the fatty acid preferably is stearic acid.

The fatty or waxy acid salts utilized in the invention are composed of achain of alkyl groups containing about 4 to about 75 carbon atoms(usually even numbered) and characterized by a —COOH terminal group. Thegeneric formula for all fatty and waxy acids above acetic acid isCH₃(CH₂)XCOOH, wherein the carbon atom count includes the carboxylgroup. The fatty or waxy acids utilized to produce the fatty or waxyacid salts incorporated into the invention may be saturated orunsaturated, and they may be present in either solid, semi-solid orliquid form.

Examples of suitable saturated fatty acids, i.e., fatty acids in whichthe carbon atoms of the alkyl chain are connected by single bonds,include but are not limited to stearic acid (C₁₈, i.e. CH₃(CH₂)₁₆COOH),palmitic acid (C₁₆, i.e., CH₃(CH₂)₁₄COOH), pelargonic acid (C₉, i.e.,CH₃(CH₂)₇COOH), and lauric acid (C₁₂, i.e., CH₃(CH₂)₁₀COOH). Examples ofsuitable unsaturated fatty acids, i.e., a fatty acid having one or moredouble bonds between the carbon atoms in the alkyl chain, include butare not limited to oleic acid (C₁₃, i.e., CH₃(CH₂)₇CH:CH(CH₂)₇COOH).

The source of the metal ions used to produce the metal salts of thefatty or waxy acid salts also incorporated into the invention aregenerally various metal salts that provide the metal ions capable ofneutralizing, to various extents, the carboxylic acid groups of thefatty acids. These include the sulfate, carbonate, acetate, andhydroxylate salts of zinc, barium, calcium, and magnesium.

Because the fatty acid salts utilized in the invention comprise variouscombinations of fatty acids neutralized with a large number of differentmetal ions, several different types of fatty acid salts may be utilizedin the invention, including metal stearates, laureates, oleates, andpalmitates, with calcium, zinc, sodium, and magnesium stearate beingpreferred, and with calcium and sodium stearate being most preferred.

The fatty or waxy acid or metal salt of the fatty or waxy acid ispresent in the modified ionomeric polymers in an amount in the range ofpreferably about 5 to about 45, more preferably about 7 to about 35, andmost preferably about 8 to about 20, weight percent (based on the totalweight of the modified ionomeric polymer).

As a result of the addition of the one or more metal salts of a fatty orwaxy acid, preferably about 40 to 100, more preferably about 50 to 100,and most preferably about 70 to 100, percent of the acidic groups in thefinal modified ionomeric polymer composition are neutralized by a metalion.

An example of such a modified ionomer polymer is DuPont® HPF-1000,available from E. I duPont de Nemours and Co. Inc.

Other examples of modified ionomeric polymers for use as theintermediate layer of the golf balls of the present invention are thoseprepared by modifying (again with one or more metal salts of a fatty orwaxy acid) ionomers based on the so-called bimodal ethylene/carboxylicacid polymers as described in U.S. Pat. No. 6,562,906, the entirecontents of which are herein incorporated by reference. These polymersare bimodal, because they result from blending two polymers of differentmolecular weights. The modified bimodal ionomeric polymers comprise:

-   -   a high molecular weight component having a molecular weight of        about 80,000 to about 500,000 and comprising one or more        ethylene/α,β-ethylenically unsaturated C₃₋₈ carboxylic acid        copolymers and/or one or more ethylene, alkyl(meth)acrylate,        (meth)acrylic acid terpolymers; wherein the high molecular        weight component is partially neutralized with metal ions        selected from the group consisting of lithium, sodium, zinc,        calcium, magnesium, and mixtures of any of these; and    -   a low molecular weight component having a molecular weight of        about 2,000 to about 30,000 and comprising one or more        ethylene/α, β-ethylenically unsaturated C₃₋₈ carboxylic acid        copolymers and/or one or more ethylene, alkyl(meth)acrylate,        (meth)acrylic acid terpolymers; wherein the low molecular weight        component is partially neutralized with metal ions selected from        the group consisting of lithium, sodium, zinc, calcium,        magnesium, and mixtures of any of these; and    -   about 5 to about 45 weight percent (based on the total weight of        the modified ionomeric polymer) of one or more fatty acids or        metal salts of a fatty acid wherein the metal is selected from        the group consisting of calcium, sodium, zinc, lithium, barium,        and magnesium, and wherein the fatty acid preferably is stearic        acid.

Again, the fatty or waxy acid salts utilized in the modified bimodalionomeric polymers are composed of a chain of alkyl groups containingabout 4 to about 75 carbon atoms (usually even numbered) andcharacterized by a —COOH terminal group. The generic formula for allfatty or waxy acids above acetic acid is CH₃(CH₂)XCOOH, wherein thecarbon atom count includes the carboxyl group. The fatty or waxy acidsutilized to produce the fatty or waxy acid salts incorporated into theinvention may be saturated or unsaturated, and they may be present ineither solid, semi-solid, or liquid form.

Examples of suitable saturated fatty acids, i.e., fatty acids in whichthe carbon atoms of the alkyl chain are connected by single bonds,include but are not limited to stearic acid (C₁₈, i.e., CH₃(CH₂)₁₆COOH),palmitic acid (C₁₆, i.e., CH₃(CH₂)₁₄COOH), pelargonic acid (C₉, i.e.,CH₃(CH₂)₇COOH), and lauric acid (C₁₂, i.e., CH₃(CH₂)₁₀COOH). Examples ofsuitable unsaturated fatty acids, i.e., a fatty acid having one or moredouble bonds between the carbon atoms in the alkyl chain, include butare not limited to oleic acid (C₁₃, i.e., CH₃(CH₂)₇CH:CH(CH₂)₇COOH).

The source of the metal ions used to produce the metal salts of thefatty or waxy acid salts also incorporated into the invention generallyare various metal salts that provide the metal ions capable ofneutralizing, to various extents, the carboxylic acid groups of thefatty acids. These include the sulfate, carbonate, acetate, andhydroxylate salts of zinc, barium, calcium, and magnesium.

Because the fatty or waxy acid salts utilized in the invention comprisevarious combinations of fatty or waxy acids neutralized with a largenumber of different metal ions, several different types of fatty acidsalts may be utilized in the invention, including metal stearates,laureates, oleates, and palmitates, with calcium, zinc, sodium, andmagnesium stearate being preferred, and with calcium and sodium stearatebeing most preferred.

The fatty or waxy acid or metal salt of the fatty or waxy acid in themodified bimodal ionomeric polymers is present in an amount ofpreferably about 5 to about 45, more preferably about 7 to about 35, andmost preferably about 8 to about 20, weight percent (based on the totalweight of the modified ionomeric polymer).

Again, as a result of the addition of the fatty or waxy acids or one ormore metal salts of a fatty or waxy acid, preferably about 40 to 100,more about 50 to 100, and most preferably about 70 to 100, percent ofthe acidic groups in the final modified bimodal ionomeric polymercomposition are neutralized by a metal ion.

In a preferred embodiment the modified ionomeric polymer compositionfurther comprises a zinc-neutralized ionomer of a polymer having thegeneral formula E/X/Y, where E is ethylene, X is a softening comonomersuch as an alkyl acrylate or methacrylate and is present in an amount ofpreferably 0 to about 50 wt. %, more preferably 0 to about 25 wt. %, andmost preferably 0 wt. %, and Y is acrylic or methacrylic acid and ispresent in an amount of preferably about 5 to about 25 wt. %, morepreferably about 10 to about 25 wt. %, and most preferably about 10 toabout 20 wt. %.

Any additional intermediate layers beyond the at least one layercomprising the material described above can comprise addition modifiedionomeric polymers or any materials as described herein for use in thecover layer of the balls of the present invention.

Additional Materials

In addition to the materials discussed above, the core, intermediatelayer, and/or the outer cover layer of the golf ball of the presentinvention can further incorporate one or more additional polymers.Examples of suitable additional polymers include, but are not limitedto, the following: thermoplastic elastomer, thermoset elastomer,synthetic rubber, thermoplastic vulcanizate, copolymeric ionomer,terpolymeric ionomer, polyurethane ionomer, polyamide ionomer,polycarbonate, polyolefin, polyamide, copolymeric polyamide, polyester,polyvinyl alcohol, acrylonitrile-butadiene-styrene copolymer,polyarylate, polyacrylate, polyphenylene ether, impact-modifiedpolyphenylene ether, high impact polystyrene, diallyl phthalate polymer,metallocene catalyzed polymer, styrene-acrylonitrile (SAN) (includingolefin-modified SAN and acrylonitrile-styrene-acrylonitrile),styrene-maleic anhydride (S/MA) polymer, styrenic copolymer,functionalized styrenic copolymer, functionalized styrenic terpolymer,styrenic terpolymer, cellulose polymer, liquid crystal polymer (LCP),ethylene-propylene-diene terpolymer (EPDM), ethylene-vinyl acetatecopolymers (EVA), ethylene-propylene copolymer, ethylene vinyl acetate,polyurea, and polysiloxane or any metallocene-catalyzed polymers ofthese species.

Suitable polyamides for use as an additional material in compositionswithin the scope of the present invention also include resins obtainedby: (1) polycondensation of (a) a dicarboxylic acid, such as oxalicacid, adipic acid, sebacic acid, terephthalic acid, isophthalic acid, or1,4-cyclohexanedicarboxylic acid, with (b) a diamine, such asethylenediamine, tetramethylenediamine, pentamethylenediamine,hexamethylenediamine, decamethylenediamine, 1,4-cyclohexyldiamine orm-xylylenediamine; (2) a ring-opening polymerization of cyclic lactam,such as ε-caprolactam or ω-laurolactam; (3) polycondensation of anaminocarboxylic acid, such as 6-aminocaproic acid, 9-aminononanoic acid,1-aminoundecanoic acid or 12-aminododecanoic acid; or (4)copolymerization of a cyclic lactam with a dicarboxylic acid and adiamine. Specific examples of suitable polyamides include nylon 6, nylon66, nylon 610, nylon 612, nylon 11, nylon 12, copolymerized nylon, nylonMXD6, and nylon 46.

Other preferred materials suitable for use as an additional material incompositions within the scope of the present invention include polyesterelastomers marketed under the trademark SKYPEL™ by SK Chemicals, ofSouth Korea, or diblock or triblock copolymers marketed under thetrademark SEPTON™ by Kuraray Corporation, of Kurashiki, Japan, andKRATON™ by Kraton Polymers Group of Companies, of Chester, UnitedKingdom. All of the materials listed above can provide for particularenhancements to ball layers prepared within the scope of the presentinvention.

The various polymer compositions used to prepare the golf balls of thepresent invention can also incorporate one or more fillers. Such fillersare typically in a finely divided form, for example, in a sizepreferably less than about 20 mesh, and more preferably less than about100 mesh, U.S. standard size, except for fibers and flock, which aregenerally elongated. Flock and fiber sizes should be small enough tofacilitate processing. Filler particle size will depend upon desiredeffect, cost, ease of addition, and dusting considerations. Theappropriate amounts of filler required will vary depending on theapplication, but typically can be readily determined without undueexperimentation.

The filler preferably is selected from the group consisting ofprecipitated hydrated silica, limestone, clay, talc, asbestos, barytes,glass fibers, aramid fibers, mica, calcium metasilicate, barium sulfate,zinc sulfide, lithopone, silicates, silicon carbide, diatomaceous earth,carbonates such as calcium or magnesium or barium carbonate, sulfatessuch as calcium or magnesium or barium sulfate, metals, includingtungsten steel copper, cobalt or iron, metal alloys, tungsten carbide,metal oxides, metal stearates, and other particulate carbonaceousmaterials, and any and all combinations thereof. Preferred examples offillers include metal oxides, such as zinc oxide and magnesium oxide. Inanother preferred embodiment the filler comprises a continuous ornon-continuous fiber. In another preferred embodiment the filler isemployed in the composition used to prepare the inner cover layer andhas a higher density than that of the modified ionomeric polymercomponent of the inner cover layer.

If desired, the various polymer compositions used to prepare the golfballs of the present invention can additionally contain otherconventional additives such as plasticizers, pigments, antioxidants,U.V. absorbers, optical brighteners, or any other additives generallyemployed in plastics formulation or the preparation of golf balls. Theappropriate amounts for these materials can be readily determinedwithout undue experimentation.

Preparation of Golf Balls

Typically the golf ball core is made by mixing together the unsaturatedpolymer, cross-linking agents, and other additives with or withoutmelting them. Dry blending equipment, such as a tumbler mixer, Vblender, ribbon blender, or two-roll mill, can be used to mix thecompositions. The golf ball compositions can also be mixed using a mill,internal mixer such as a Banbury or Farrel continuous mixer, extruder orcombinations of these, with or without application of thermal energy toproduce melting. The various core components can be mixed together withthe cross-linking agents, or each additive can be added in anappropriate sequence to the milled unsaturated polymer. In anothermethod of manufacture the cross-linking agents and other components canbe added to the unsaturated polymer as part of a concentrate using dryblending, roll milling, or melt mixing. If radiation is a cross-linkingagent, then the mixture comprising the unsaturated polymer and otheradditives can be irradiated following mixing, during forming into a partsuch as the core of a ball, or after forming.

The resulting mixture can be subjected to, for example, a compression orinjection molding process, to obtain solid spheres for the core. Thepolymer mixture is subjected to a molding cycle in which heat andpressure are applied while the mixture is confined within a mold. Thecavity shape depends on the portion of the golf ball being formed. Thecompression and heat liberates free radicals by decomposing one or moreperoxides, which initiate cross-linking. The temperature and duration ofthe molding cycle are selected based upon the type of peroxide andpeptizer selected. The molding cycle may have a single step of moldingthe mixture at a single temperature for fixed time duration.

For example, a preferred mode of preparation for the cores used in thepresent invention is to first mix the core ingredients on a two-rollmill, to form slugs of approximately 30-40 g, and then compression-moldin a single step at a temperature between 150 to 180° C., for a timeduration between 5 and 12 minutes.

The various core components may also be combined to form a golf ball byan injection molding process, which is also well known to one ofordinary skill in the art. The curing time depends on the variousmaterials selected, and those of ordinary skill in the art will bereadily able to adjust the curing time upward or downward based on theparticular materials used and the discussion herein.

The various formulations for the intermediate layer and/or cover layermay be produced using a twin-screw extruder or may be blended manuallyor mechanically prior to the addition to the injection molder feedhopper. Finished golf balls may be prepared by initially positioning thesolid, preformed core in an injection-molding cavity, followed byuniform injection of the intermediate layer and/or cover layercomposition sequentially over the core. The cover formulations can beinjection molded around the cores to produce golf balls of the requireddiameter.

Alternatively, the cover layers may also be formed around the core byfirst forming half shells by injection molding followed by compressionmolding the half shells about the core to form the final ball.

Covers may also be formed around the cores using compression molding.Cover materials for compression molding may also be extruded or blendedresins or castable resins such as polyurethane.

Ball Construction Properties

The core 12 of the golf ball 10 of the present invention has a diameterof preferably about 1.20 to about 1.56 in., more preferably about 1.40to about 1.52 in., and most preferably about 1.45 to about 1.50 in. Thecore also has a PGA compression of preferably about 40 to about 90, morepreferably about 40 to about 85, and most preferably about 40 to about80.

The intermediate layer 14 of the golf ball 10 of the present inventionhas a thickness of preferably about 0.01 to about 0.10 in., morepreferably about 0.02 to about 0.08 in., and most preferably about 0.03to about 0.06 in. The intermediate layer also has a Shore D hardness inthe range of preferably about 30 to about 75, more preferably about 40to about 70, and most preferably about 40 to about 65. The intermediatelayer also has an average acid content of about 5 to about 25 wt. %(based on the total weight of the intermediate layer composition).

The cover layer 16 of the golf ball 10 of the present invention has athickness in the range of preferably about 0.01 to about 0.10 in., morepreferably about 0.02 to about 0.08 in., and most preferably about 0.03to about 0.06 in. The cover layer also has a Shore D hardness in therange of preferably about 40 to about 70, more preferably about 45 toabout 70, and most preferably about 50 to about 70.

The C.O.R. of the golf balls 10 of the present invention preferably isgreater than about 0.790, more preferably is greater than about 0.795,and most preferably is greater than about 0.800, at an inbound velocityof 125 ft/sec.

EXAMPLES

Examples of the invention are given below by way of illustration and notby way of limitation.

Core Components and Preparation

A series of ball cores having diameters of 1.48 in., and suitable foruse in golf balls within the scope of the present invention wereprepared. Each core used the following materials:

BR40 is a cis-1,4-polybutadiene rubber made with a rare earth catalystand is commercially available from Enichem (Italy).

ZnO is a rubber grade zinc oxide commercially available from Akrochem(Akron, Ohio).

ZDA is zinc diacrylate and is commercially available from Sartomer.Several grades are available, which may be used interchangeably or incombination.

Varox 231XL is 1,1-di(t-butylperoxy)-3,3,5-trimethyl-cyclohexane is across-linking initiator (40% active peroxide). This is commerciallyavailable from R.T. Vanderbilt (Norwalk, Conn.).

The cores each incorporated as the base rubber, cis-1,4-polybutadiene.Additionally, the cores incorporated zinc oxide, zinc diacrylate, and aperoxide cross-linking initiator.

The core ingredients were mixed on a two-roll mill, and slugs ofapproximately 34.5 g were formed and compression-molded at 170° C. forseven minutes. The resulting cores were then tested for C.O.R. and PGAcompression after one day of aging at room temperature. Detailedcomposition information for the cores is provided below in Table 1.

TABLE 1 Varox BR40 ZnO ZDA 231XL (pph*) (pph) (pph) (pph)** 100 26 300.8 *pph = parts per hundred of unsaturated polymer **active peroxide =0.32 pph

Inner and Outer Cover Layer Components

The materials employed in the blend formulations used for the innercover layer and/or the outer cover layer were as follows:

DuPont® HPF-1000 is a grade of polymer commercially available fromDuPont having a melt flow index (as measured by ASTM D1238, 190° C./2.16kg) of 0.65 g/10 min and a density (ASTM D1003) of 0.96 g/cm³.

Septon HG 252 is a triblock copolymer having polystyrene end blocks anda hydrogenated polyisoprene midblock and has hydroxyl groups at the endof the polystyrene blocks. HG-252 is commercially available from KurarayAmerica Inc. (Houston, Tex.).

Pebax® 3533 is a polyether amide block copolymer commercially availablefrom Atofina.

Surlyn® 9120 is a grade of ionomer commercially available from DuPont,and it is a zinc ionomer of an ethylene/methacrylic acid polymer.

Surlyn 8140 is a grade of ionomer commercially available from DuPont,and it is a sodium ionomer of an ethylene/methacrylic acid polymer.

Surlyn® 8320 is a grade of ionomer commercially available from DuPont,and it is a sodium ionomer of an ethylene/methacrylic acid/methacrylatepolymer.

In addition, a color concentrate (“CC”) was used in some of the blendformulations. It consisted of 50 wt. % TiO2 and 50 wt. % of athermoplastic binder. Such a concentrate is commercially available fromCarolina Color Corporation.

Intermediate and Cover Material Preparation

By blending the ingredients set forth in the Table 2 below, a series ofplastic formulations for use in either the intermediate layer or thecover layer were produced using a twin-screw extruder.

Final Ball Preparation

Finished golf balls were prepared by positioning the solid, preformedcross-linked polybutadiene core in an injection molding cavity, followedby uniform injection of the selected intermediate layer or cover layercomposition sequentially over the core. The intermediate and cover layerformulations were injection-molded around the identical solid type coresof finished diameter of 1.48 inches, to produce golf balls ofapproximately 1.680 inches in diameter having the ball constructions andproperties as summarized in Table 2.

The ball's dimple pattern included 442 dimples.

The properties of PGA compression, coefficient of restitution (C.O.R.),Shore D hardness, and other tests on either the materials or theresulting balls were conducted using the test methods as defined below.

Core or ball diameter was determined by using standard linear calipersor size gauge.

Core specific gravity was determined by electronic densimeter using ASTMD-792.

Compression was measured by applying a spring-loaded force to the golfball center, golf ball core, or the golf ball to be examined, with amanual instrument (an “Atti gauge”) manufactured by the Atti EngineeringCompany of Union City, N.J. This machine, equipped with a Federal DialGauge, Model D81-C, employs a calibrated spring under a known load. Thesphere to be tested is forced a distance of 0.2 inch (5 mm) against thisspring. If the spring, in turn, compresses 0.2 inch, then thecompression is rated at 100; if the spring compresses 0.1 inch, then thecompression value is rated as 0. Thus, more compressible, softermaterials will have lower Atti gauge values than will harder, lesscompressible materials. Compression measured with this instrument isalso referred to as PGA compression. The approximate relationship thatexists between Atti or PGA compression and Riehle compression can beexpressed as:

(Atti or PGA compression)=(160-Riehle Compression).

Thus, a Riehle compression of 100 would be the same as an Atticompression of 60.

Coefficient of restitution (C.O.R.) of the cores or balls was measuredusing an air cannon to fire the core or ball, at an inbound velocity of125 feet per second, against a steel plate positioned 81 inches from thecannon's muzzle. The rebound velocity was then measured via a timingmechanism using three light gates. The rebound velocity was divided bythe inbound velocity to yield the coefficient of restitution.

Shore D hardness was measured in accordance with ASTM Test D2240, exceptthat the hardness was determined perpendicular to the curved surface ofthe core or on the land area between dimples on the surface of the ball.

The ball performance was determined using a Robot Driver Test, whichutilized a commercial swing robot in conjunction with an optical systemto measure ball speed, launch angle, and backspin. In this test, atitanium driver was attached to a swing robot, and the swing speed andpower profile, as well as the tee location and club lie angle, wereset-up to generate the values set forth below. A Maxfli XS Tour golfball was used as a reference:

Headspeed: 112 mph

Ballspeed: 160 mph

Launch Angle: 9 deg

Backspin: 3200 rpm

The test ball was substituted for the reference ball and thecorresponding values determined as summarized in Table 2. Example 1 andComparative Example 1 both shared the same core and cover compositions,and both had a similar cover hardness of 62 Shore D. Similarly, Example2 and Comparative 2 both shared the same core and cover compositions,and both had a similar cover hardness of 58 Shore D and similar PGA ballcompression.

Comparison of the resulting ball performance data in Table 2demonstrates that both Examples 1 and 2 had higher driver speed andhigher C.O.R. than did Comparative Examples 1 and 2, respectively,despite having the identical core compression and C.O.R. and havingidentical cover hardnesses.

Thus the combination of the use of a modified ionomeric polymer in aninner cover layer of the specified hardness and thickness in amulti-layer golf ball, allows production of a ball having increaseddriver velocity, and lower driver spin (hence improved distance) for agiven core compression and outer cover layer hardness, therebymaintaining the ball feel.

TABLE 2 Ex 1 Ex 2 Comp Ex 1 Comp Ex 2 Core diameter (in) 1.48 1.48 1.481.48 Core Specific Gravity 1.19 1.19 1.19 1.19 Core Compression (PGA) 7070 70 70 Core C.O.R. 0.80 0.80 0.80 0.80 Inter. Layer Comp. (wt. %)DuPont ® HPF- DuPont ® HPF- Pebax ® 3533 (70) Pebax ® 3533 (70) 1000(100) 1000 (100) Surlyn ® 9120 (15) Surlyn ® 9120 (15) Surlyn ® 8140(15) Surlyn ® 8140 (15) Inter. Layer Thickness (in.) 0.050 0.050 0.0500.050 Inter. Layer Hardness 50 50 40 40 (Shore D) Cover Layer Comp. (wt.%) Surlyn ® 8140 (30) Surlyn ® 8140 (22) Surlyn ® 8140 (30) Surlyn ®8140 (22) Surlyn ® 9120 (30) Surlyn ® 9120 (22) Surlyn ® 9120 (30)Surlyn ® 9120 (22) Surlyn ® 8320 (35) Surlyn ® 8320 (48) Surlyn ® 8320(35) Surlyn ® 8320 (48) CC (5) HG 252 (3) CC (5) HG 252 (3) CC (5) CC(5) Cover Layer Thickness (in.) 0.050 0.050 0.050 0.050 Cover LayerHardness 62 58 62 58 (Shore D) Ball Pole Size (in) 1.685 1.685 1.6851.685 Ball Equator Size (in) 1.685 1.685 1.685 1.685 Ball Compression(PGA) 85-90 80-85 80-85 75-80 Ball C.O.R. 0.810-0.815 0.805-0.810 0.8000.792 Driver Ball Speed (mph) 163.7 163.1 162.8 161.8 Driver Ball Launchangle (°) 9.2 9.3 9.2 8.9 Driver Ball Spin (rpm) 3000 3000 3050 3250

1. A golf ball comprising: a. a core, wherein said core comprises acenter and one or more layers disposed around said center, and whereinthe difference between the hardness of one layer and the next adjacentlayer is greater than 2 Shore D units; b. an intermediate layer; and c.a cover layer; d. wherein said intermediate layer comprises a modifiedionomeric polymer comprising a blend composition comprising: (1)ethylene, (2) 5 to 25 weight percent (meth)acrylic acid (based on thetotal weight of (1), (2), and (3)), and (3) 0 to 40 weight percent of aC₁ to C₈-alkyl acrylate (based on the total weight of (1), (2), and(3)), and (4) about 5 to about 45 weight percent (based on the totalweight of said modified ionomeric polymer), of a fatty acid or one ormore metal salts of said fatty acid, wherein therein about 40 to 100percent of the acid groups present in said modified ionomeric polymerare neutralized with zinc, sodium, lithium, calcium, or magnesium ions,or a combination thereof; e. wherein said core has a diameter in therange of about 1.20 to about 1.56 in. and a PGA compression in the rangeof about 40 to about 90; f. wherein said intermediate layer has athickness in the range of about 0.01 to about 0.10 in. and a Shore Dhardness in the range of about 30 to about 75; g. and wherein said coverlayer has a Shore D hardness in the range of about 40 to about 70; andwherein the golf ball has a coefficient of restitution greater than0.800, at 125 ft/sec inbound velocity.
 2. The golf ball of claim 1,wherein: a. said core has a diameter in the range of about 1.40 to about1.52 in. and a PGA compression in the range of about 40 to about 85; b.said modified ionomeric polymer present in the intermediate layercomprises about 7 to about 35 weight percent (based on the total weightof said modified ionomeric polymer) of said one or more fatty acids ormetal salts of a fatty acid, said metal being selected from the groupconsisting of calcium, sodium, zinc, lithium, magnesium, barium, andcombinations thereof; c. about 50 to 100 percent of the acid groupspresent in said modified ionomeric polymer present in the intermediatelayer are neutralized with zinc, sodium, lithium, calcium, or magnesiumions, or a combination thereof; d. said intermediate layer has athickness in the range of about 0.02 to about 0.08 in and a Shore Dhardness in the range of about 40 to about 70; and e. said cover layerhas a Shore D hardness in the range of about 45 to about
 70. 3. The golfball of claim 1, wherein: a. said core has a diameter of about 1.45 toabout 1.50 in. and a PGA compression of about 40 to about 80; b. themodified ionomeric polymer present in said intermediate layer comprisesabout 8 to about 20 weight percent (based on the total weight of themodified ionomeric polymer) of one or more or metal salts of stearicacid, said metal being selected from the group consisting of calcium,sodium, zinc, lithium, magnesium, barium, and combinations thereof; c.about 70 to 100 percent of the acid groups present in said modifiedionomeric polymer of said intermediate layer are neutralized with zinc,sodium, lithium, calcium, or magnesium ions, or a combination thereof;d. said intermediate layer has a thickness in the range of about 0.03 toabout 0.06 in., a Shore D hardness in the range of about 40 to about 65,and an average acid content of in the range of about 5 to about 25weight percent; and e. said cover layer has a Shore D hardness in therange of about 50 to about
 70. 4. The golf ball of claim 1, wherein saidmodified ionomeric polymer further comprises a zinc-neutralized ionomerof a polymer having the general formula E/X/Y, where E is ethylene, X isan alkyl(meth)acrylate present in an amount in the range of 0 to about50 weight percent (based on the total weight of said zinc-neutralizedionomer), and Y is (meth)acrylic acid present in an amount in the rangeof about 5 to about 25 weight percent (based on the total weight of saidzinc-neutralized ionomer).
 5. The golf ball according to claim 1,wherein said core comprises: a. at least one unsaturated polymer; b. atleast one cross-linking agent; and c. at least one co-cross-linkingagent.
 6. The golf ball according to claim 5, wherein: a. saidunsaturated polymer has a Mooney viscosity (ML₁₊₄ (100° C.)) in therange of about 20 to about 80 and is selected from the group consistingof 1,2-polybutadiene, cis-1,4-polybutadiene, trans-1,4-polybutadiene,cis-polyisoprene, trans-polyisoprene, polychloroprene, polybutylene,styrene-butadiene rubber, styrene-butadiene-styrene block copolymer andpartially and fully hydrogenated equivalents, styrene-isoprene-styreneblock copolymer and partially and fully hydrogenated equivalents,nitrile rubber, silicone rubber, polyurethane, and combinations thereof;and b. said cross-linking agent is present in an amount in the range ofabout 0.05 to about 5 parts by weight of the cross-linking agents per100 parts by weight of the unsaturated polymer.
 7. The golf ballaccording to claim 6, wherein said core further comprises a peptizercomprising an organic sulfur compound, a metal salt of an organic sulfurcompound, and/or a non-metal salt of an organic sulfur compound.
 8. Thegolf ball according to claim 7, wherein said core comprises: a. a firstcross-linking agent having a first characteristic decompositiontemperature less than 150° C. for a t_(1/2) equal to 0.1 hour; and b. asecond cross-linking agent having a second characteristic decompositiontemperature greater than 150° C. for a t_(1/2) equal to 0.1 hour.
 9. Thegolf ball according to claim 8, wherein the composition weight ratio ofthe first cross-linking agent to the second cross-linking agent is inthe range of 5:95 to 95:5.
 10. The golf ball according to claim 8,wherein the composition weight ratio of the first cross-linking agent tothe second cross-linking agent is in the range of 10:90 to 50:50. 11.The golf ball according to claim 6, wherein said core further comprisesan accelerator present in an amount in the range of about 0.1 to about10 parts by weight per 100 parts by weight of said unsaturated polymer.12. The golf ball according to claim 6, wherein said core furthercomprises a filler selected from the group consisting of precipitatedhydrated silica, limestone, clay, talc, asbestos, barytes, glass fibers,aramid fibers, mica, calcium metasilicate, barium sulfate, zinc sulfide,lithopone, silicates, silicon carbide, diatomaceous earth, calciumcarbonate, magnesium carbonate, barium carbonate, calcium sulfate,magnesium sulfate, barium sulfate, tungsten, steel, copper, cobalt oriron, metal alloys, tungsten carbide, metal oxides, metal stearates,particulate carbonaceous materials, and any and all combinationsthereof.
 13. The golf ball according to claim 5, wherein: a. saidunsaturated polymer is cis-1,4-polybutadiene and has a Mooney viscosity(ML₁₊₄ (100° C.)) in the range of about 30 to about 70; and b. saidcross-linking agent is present in an amount in the range of about 0.2 toabout 3 parts by weight per 100 parts by weight of the unsaturatedpolymer.
 14. The golf ball according to claim 13, wherein said corefurther comprises a peptizer comprising: a. an organic sulfur compoundor metal salt of an organic sulfur compound, present in an amount in therange of about 0.01 to about 10 parts by weight per 100 parts by weightof the unsaturated polymer; or b. a non-metal salt of an organic sulfurcompound, present in an amount in the range of about 0.01 to about 10parts by weight per 100 parts by weight of the unsaturated polymer. 15.The golf ball according to claim 13, wherein said core further comprisesan accelerator present in an amount in the range of about 0.2 to about 5parts by weight per 100 parts by weight of the unsaturated polymer. 16.The golf ball according to claim 5, wherein: a. said unsaturated polymeris cis-1,4-polybutadiene and has a Mooney viscosity (ML1+4 (100° C.)) inthe range of about 35 to about 50; and b. said cross-linking agent ispresent in an amount in the range of about 0.2 to about 2 parts byweight per 100 parts by weight of the unsaturated polymer.
 17. The golfball according to claim 16, wherein said core further comprise apeptizer comprising: a. pentachlorothiophenol, dibenzamidodiphenyldisulfide, or a metal salt of pentachlorothiophenol, present inan amount in the range of about 0.10 to about 7 parts by weight per 100parts by weight of the unsaturated polymer; or b. an ammonium salt ofpentachlorothiophenol, with the ammonium cation having the generalcycloaliphatic or aromatic system, or a combination thereof, present inan amount in the range of about 0.1 to about 7 parts by weight per 100parts by weight of the unsaturated polymer.
 18. The golf ball accordingto claim 17, wherein said peptizer is pentachlorothiophenol, or the zincsalt of pentachlorothiophenol, and is present in an amount in the rangeof about 0.15 to about 5 parts by weight per 100 parts by weight of saidunsaturated polymer.
 19. (canceled)
 20. The golf ball according to claim16, wherein said core further comprises an accelerator present in anamount in the range of about 0.5 to about 1.5 parts by weight per 100parts by weight of the unsaturated polymer, and wherein the acceleratoris selected from the group consisting of 2-mercaptobenzothiazole and asalt of 2-mercaptobenzothiazole.
 21. The golf ball according to claim 5,wherein said core comprises: a. a first cross-linking agent having afirst characteristic decomposition temperature less than 150° C. for at1/2 equal to 0.1 hour; and b. a second cross-linking agent having asecond characteristic decomposition temperature greater than 150° C. fora t_(1/2) equal to 0.1 hour.
 22. The golf ball according to claim 21,wherein the composition weight ratio of the first cross-linking agent tothe second cross-linking agent is in the range of 5:95 to 95:5.
 23. Thegolf ball according to claim 21, wherein the composition weight ratio ofthe first cross-linking agent to the second cross-linking agent is inthe range of 10:90 to 50:50.
 24. (canceled)
 25. The golf ball of claim1, wherein said cover layer further comprises a zinc-neutralized ionomerof a polymer having the general formula E/X/Y, where E is ethylene, X isan alkyl(meth)acrylate present in an amount in the range of 0 to about50 weight percent (based on the total weight of said zinc-neutralizedionomer), and Y is (meth)acrylic acid present in an amount in the rangeof about 5 to about 25 weight percent (based on the total weight of saidzinc-neutralized ionomer).
 26. (canceled)
 27. The golf ball according toclaim 1, wherein one or more of said core, said intermediate layer, orsaid cover layer further comprises a polymer selected from the groupconsisting of thermoplastic elastomers, thermoset elastomers, syntheticrubber, thermoplastic vulcanizates, polycarbonate, polyolefin,polyamide, copolymeric polyamide, polyesters, polyvinyl alcohols,acrylonitrile-butadiene-styrene copolymers, polyarylate, polyacrylate,polyphenylene ether, impact-modified polyphenylene ether, high impactpolystyrene, diallyl phthalate polymer, metallocene catalyzed polymers,styrene-acrylonitrile (SAN) (including olefin-modified SAN andacrylonitrile-styrene-acrylonitrile), styrene-maleic anhydride (S/MA)polymer, styrenic copolymer, functionalized styrenic copolymer,functionalized styrenic terpolymer, styrenic terpolymer, cellulosepolymer, liquid crystal polymer (LCP), ethylene-propylene-dieneterpolymer (EPDM), ethylene-vinyl acetate copolymers (EVA),ethylene-propylene copolymer, ethylene vinyl acetate, polyurea, andpolysiloxane, or any metallocene-catalyzed polymers of these species.28-30. (canceled)
 31. The golf ball according to claim 1, wherein thespecific gravity increases outwards, from the center to the outermostcore layer.
 32. The golf ball according to claim 1, wherein the specificgravity decreases outwards, from the center to the outermost core layer.33. The golf ball according to claim 1, wherein said core comprises acenter and one or more layers disposed around said center, and whereinthe difference between the specific gravity of one layer and the nextadjacent layer is greater than 0.1.
 34. (canceled)
 35. The golf ballaccording to claim 33, wherein said cover layer further comprises azinc-neutralized ionomer of a polymer having the general formula E/X/Y,where E is ethylene, X is an alkyl(meth)acrylate present in an amount inthe range of 0 to about 50 weight percent (based on the total weight ofsaid zinc-neutralized ionomer), and Y is (meth)acrylic acid present inan amount in the range of about 5 to about 25 weight percent (based onthe total weight of said zinc-neutralized ionomer).
 36. A golf ballcomprising: a. a core, wherein said core comprises a center and one ormore layers disposed around said center, and wherein the differencebetween the specific gravity of one layer and the next adjacent layer isgreater than 0.1; b. an intermediate layer; and c. a cover layer; d.wherein said intermediate layer comprises a modified ionomeric polymercomprising: a blend composition comprising: (1) ethylene, (2) 5 to 25weight percent (meth)acrylic acid (based on the total weight of (1),(2), and (3)), and (3) 0 to 40 weight percent of a C₁ to C₈-alkylacrylate (based on the total weight of (1), (2), and (3)), and (4) about5 to about 45 weight percent (based on the total weight of said modifiedionomeric polymer), of a fatty acid or one or more metal salts of saidfatty acid, wherein about 40 to 100 percent of the acid groups presentin said modified ionomeric polymer are neutralized with zinc, sodium,lithium, calcium, or magnesium ions, or a combination thereof; e.wherein said core has a diameter in the range of about 1.20 to about1.56 in. and a PGA compression in the range of about 40 to about 90; f.wherein said intermediate layer has a thickness in the range of about0.01 to about 0.10 in. and a Shore D hardness in the range of about 30to about 75; g. wherein said cover layer has a Shore D hardness in therange of about 40 to about 70; and wherein the golf ball has acoefficient of restitution greater than 0.800, at 125 ft/sec inboundvelocity.
 37. The golf ball of claim 36, wherein: a. said core has adiameter in the range of about 1.40 to about 1.52 in. and a PGAcompression in the range of about 40 to about 85; b. said modifiedionomeric polymer present in the intermediate layer comprises about 7 toabout 35 weight percent (based on the total weight of said modifiedionomeric polymer) of said one or more fatty acids or metal salts of afatty acid, said metal being selected from the group consisting ofcalcium, sodium, zinc, lithium, magnesium, barium, and combinationsthereof; c. about 50 to 100 percent of the acid groups present in saidmodified ionomeric polymer present in the intermediate layer areneutralized with zinc, sodium, lithium, calcium, or magnesium ions, or acombination thereof; d. said intermediate layer has a thickness in therange of about 0.02 to about 0.08 in and a Shore D hardness in the rangeof about 40 to about 70; and e. said cover layer has a Shore D hardnessin the range of about 45 to about 70.